The limitations of many IoT devices in terms of storage, computing power and energy consumption make them require to be connected to other devices when needing to perform computationally intensive tasks, like it happens with IoT systems based on Edge Computing architectures. However, the lack of wireless connectivity in the places where IoT nodes are deployed or where they move through is still a problem. One of the solutions to mitigate this problem consists in using opportunistic networks, which provide connectivity and processing resources efficiently while reducing the communications traffic with remote clouds. Thus, opportunistic networks are helpful in situations when wireless communication coverage is not available, like it occurs in certain rural areas, during natural disasters, in wars or when other factors cause network disruptions, as well as in other IoT scenarios where the cloud becomes saturated (for example, due to an excessive amount of concurrent communications or when Denial-of-Service (DoS) attacks occur). This article presents the design and initial validation of a novel Opportunistic Edge Computing (OEC) system based on Bluetooth 5 and on the use of low-cost Single-Board Computers (SBCs). After describing the proposed OEC system, several test results are presented for different IoT scenarios where IoT nodes travel inside vehicles. Specifically, latency and packet loss are measured thanks to the use of an experimental testbench made of two separate IoT networks (each one consisted of an IoT node and an OEC gateway): one located in a remote office and another one inside a moving vehicle, which was driven at different vehicular speeds. The obtained results show that the developed system is able to obtain sufficiently low latency values in the selected scenarios and at low-to-medium vehicular speeds, which makes the proposed system useful for OEC applications for urban roads and with low latency requirements.